626 research outputs found
Synthesis of Two Key Fragments of the Complex Polyhalogenated Marine Meroterpenoid Azamerone
A concise route toward two advanced fragments in the context of the total synthesis of the unique natural product azamerone is reported. Key synthetic features include the enantioselective synthesis of an epoxysilane and its Lewis-acid-induced cyclization and the installation of the pyridazine ring via a formylation/condensation sequence. This route provides strategic insights into the chemistry of phthalazinediols, facilitating synthetic approaches toward this class of natural products
Microwave Lens for Polar Molecules
We here report on the implementation of a microwave lens for neutral polar
molecules suitable to focus molecules both in low-field-seeking and in
high-field-seeking states. By using the TE_11m modes of a 12 cm long
cylindrically symmetric microwave resonator, Stark-decelerated ammonia
molecules are transversally confined. We investigate the focusing properties of
this microwave lens as a function of the molecules' velocity, the detuning of
the microwave frequency from the molecular resonance frequency, and the
microwave power. Such a microwave lens can be seen as a first important step
towards further microwave devices, such as decelerators and traps.Comment: 4 pages, 3 figure
Cross-Coupling Reactions of Monosubstituted Tetrazines
A Ag-mediated Pd-catalyzed cross-coupling method for 3-bromo-1,2,4,5-tetrazine with boronic acids is presented. Electronic modification of the 1,1′-bis(diphenylphosphine)ferrocene (dppf) ligand was found to be crucial for good turnover. Using this fast method, a variety of alkyl-, heteroatom-, and halide-substituted aryl- and heteroaryl-tetrazines were prepared (29 examples, up to 87% yield)
Boron Trifluoride-Mediated Cycloaddition of 3-Bromotetrazine and Silyl Enol Ethers: Synthesis of 3-Bromo-pyridazines
Pyridazines are important scaffolds for medicinal chemistry or crop protection agents, yet the selective preparation of 3-bromo-pyridazines with high regiocontrol remains difficult. We achieved the Lewis acid-mediated inverse electron demand Diels–Alder reaction between 3-monosubstituted s-tetrazine and silyl enol ethers and obtained functionalized pyridazines. In the case of 1-monosubstituted silyl enol ethers, exclusive regioselectivity was observed. Downstream functionalization of the resulting 3-bromo-pyridazines was demonstrated utilizing several cross-coupling protocols to synthesize 3,4-disubstituted pyridazines with excellent control over the substitution pattern
Diffusion in low-dimensional lipid membranes
The diffusion behavior of biological components in cellular membranes is vital to the function of cells. By collapsing the complexity of planar 2D membranes down to one dimension, fundamental investigations of bimolecular behavior become possible in one dimension. Here we develop lipid nanolithography methods to produce membranes, under fluid, with widths as low as 6 nm but extending to microns in length. We find reduced lipid mobility, as the width is reduced below 50 nm, suggesting different lipid packing in the vicinity of boundaries. The insertion of a membrane protein, M2, into these systems, allowed characterization of protein diffusion using high-speed AFM to demonstrate the first membrane protein 1D random walk. These quasi-1D lipid bilayers are ideal for testing and understanding fundamental concepts about the roles of dimensionality and size on physical properties of membranes from energy transfer to lipid packing
The Buffer Gas Beam: An Intense, Cold, and Slow Source for Atoms and Molecules
Beams of atoms and molecules are stalwart tools for spectroscopy and studies
of collisional processes. The supersonic expansion technique can create cold
beams of many species of atoms and molecules. However, the resulting beam is
typically moving at a speed of 300-600 m/s in the lab frame, and for a large
class of species has insufficient flux (i.e. brightness) for important
applications. In contrast, buffer gas beams can be a superior method in many
cases, producing cold and relatively slow molecules in the lab frame with high
brightness and great versatility. There are basic differences between
supersonic and buffer gas cooled beams regarding particular technological
advantages and constraints. At present, it is clear that not all of the
possible variations on the buffer gas method have been studied. In this review,
we will present a survey of the current state of the art in buffer gas beams,
and explore some of the possible future directions that these new methods might
take
Search for and a measurement of the branching fraction for
We search for the decay and measure the
branching fraction for using
121.4~ of data collected at the
resonance with the Belle detector at the KEKB asymmetric-energy
collider. The branching fraction is measured
to be , where is the fraction of
in events. Our result is in good
agreement with the theoretical predictions as well as with a recent measurement
from LHCb. We observe no statistically significant signal for the decay
and set a confidence-level upper
limit on its branching fraction at . This constitutes a
significant improvement over the previous result.Comment: 6 pages, 3 figure
Search for a dark vector gauge boson decaying to using decays
We report a search for a dark vector gauge boson that couples to
quarks in the decay chain , . No signal is found and we set a
mass-dependent limit on the baryonic fine structure constant of in the mass range of 290 to 520 MeV/. This analysis is
based on a data sample of 976 fb collected by the Belle experiment at
the KEKB asymmetric-energy collider.Comment: 6 pages, 4 figure
Search for decays to invisible final states at Belle
We report the result from the first search for decays to invisible
final states. The analysis is performed on a data sample of 924
collected at and near the and resonances with the
Belle detector at the KEKB asymmetric-energy collider. The
absolute branching fraction is determined using an inclusive sample,
obtained by fully reconstructing the rest of the particle system including the
other charmed particle. No significant signal yield is observed and an upper
limit of is set on the branching fraction of to
invisible final states at 90\% confidence level.Comment: 17 pages, 4 figures, submitted to PRD(RC
Search for the decay at Belle
We report a search for the rare charmless decay
using a data sample of
pairs collected at the resonance with
the Belle detector at the KEKB asymmetric-energy collider. No
statistically significant signal is found and a 90% confidence-level upper
limit is set on the decay branching fraction as .Comment: 8 pages, 3 figures, submitted to PRD(RC
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